A pustule is a small, raised bump on the skin that is filled with pus. It often appears red and inflamed around the edges. Pustules can be a symptom of various skin conditions, including acne, eczema, and psoriasis. They can occur anywhere on the body but are most commonly found on the face, back, and shoulders. Pustules develop when hair follicles become clogged with oil, dead skin cells, and bacteria. This blockage leads to inflammation and the formation of pus. While they are generally not serious, pustules can be uncomfortable and may require treatment to prevent scarring or infection.